Set-back rocket motor ignitor for shoulder-fired rockets

ABSTRACT

A rocket motor ignitor assembly that may be used in a shoulder-fired rocket system. The rocket motor ignitor assembly may include a delay ignitor operable to ignite a rocket motor propellant, a stab firing pin operable to activate the delay ignitor by contacting the delay ignitor, and a biasing element coupled with the stab firing pin. The stab firing pin may have a length to diameter ratio greater than two, as well as relief grooves allowing air to vent past the stab firing pin as it travels toward the delay ignitor to activate it. The rocket motor ignitor assembly may also include a guide stop to limit penetration of the stab firing pin into the delay ignitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/742,415, filed Oct. 7, 2018, the contents of which are incorporated by reference herein in their entirety.

FIELD

The present disclosure is broadly concerned with shoulder-fired rockets and shoulder-fired rocket systems. In particular, the present disclosure is related to set-back rocket motor ignitor assemblies for use in shoulder-fired rockets and should-fired rocket systems.

BACKGROUND

Shoulder-fired rockets, including, for example, Rocket Propelled Grenades (RPGs) have been known to suffer from reliability, safety, and accuracy issues. Improved shoulder-fired rockets, and in particular, rocket motor ignitor assemblies having improved features are desirable.

BRIEF DESCRIPTION OF THE FIGURES

The embodiments herein may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate analogous, identical, or functionally similar elements. Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings.

FIG. 1 illustrates a top view of a shoulder-fired rocket system including a warhead, a rocket motor that includes a rocket motor ignitor assembly, and an expelling charge, according to at least one instance of the present disclosure.

FIG. 2 depicts an exploded view of a shoulder-fired rocket system including a warhead, a rocket motor that includes a rocket motor ignitor assembly, and an expelling charge, according to at least one instance of the present disclosure.

FIG. 3 depicts a cross-sectional view of a rocket motor assembly having a rocket motor ignitor assembly, according to at least one instance of the present disclosure.

FIG. 4 depicts an exploded view of a rocket motor ignitor assembly, according to at least one instance of the present disclosure.

FIG. 5A depicts a rocket motor ignitor assembly in a pre-fired (ready) condition, according to at least one instance of the present disclosure.

FIG. 5B depicts a rocket motor ignitor assembly in a firing condition, according to at least one instance of the present disclosure.

FIG. 6 depicts a plan view of a rocket motor ignitor assembly, according to at least one instance of the present disclosure.

FIG. 7 depicts a stab firing pin having relief grooves, according to at least one instance of the present disclosure.

DETAILED DESCRIPTION

The present disclosure provides rocket motor assemblies having rocket motor ignitor assemblies that may be used in shoulder-fired rocket systems including, but not limited to, rocket propelled grenade systems and apparatus. In particular, a rocket motor ignitor assembly is provided that includes a delay ignitor operable to ignite a rocket motor propellant, a stab firing pin operable to activate the delay ignitor by contacting the delay ignitor, and a biasing element coupled with the stab firing pin. The delay ignitor may be operable to ignite the rocket motor propellant after a predetermined amount of time upon activation by the stab firing pin. The biasing element is biased to space apart the stab firing pin and the delay ignitor when the rocket motor ignitor assembly is in a pre-fired condition. When the rocket motor ignitor assembly is in a firing condition, the biasing element is operable to be overcome to allow the stab firing pin to contact the delay ignitor.

According to at least one aspect of the present disclosure, the stab firing pin may have a length to diameter ratio greater than two (2). In some instances, the length to diameter ratio of the stab firing pin is greater than two and a half (2.5) or greater than three (3). A stab firing pin having a length to diameter ratio greater than two (2) ensures that the stab firing pin stays straight as it travels down the ignitor tube body, thus improving the reliability of rocket motor assembly.

According to at least one aspect of the present disclosure, the stab firing pin of the rocket motor ignitor assembly comprises relief grooves operable to vent air around the edge of the stab firing pin as the stab firing pin travels toward the delay ignitor. In some instances, the relief grooves may be helical relief grooves cut into the side of the stab firing pin. The relief grooves are operable to prevent the stab firing pin from compressing air as it travels towards the delay ignitor and thus serve to improve reliability of the rocket motor ignitor assembly by reducing the probability of the stab firing pin from becoming stuck or otherwise retarded during its rearward travel towards the delay ignitor.

According to at least one aspect of the present disclosure, the rocket motor ignitor assembly also includes a guide stop having an inner bore operable to receive the stab firing pin so as to limit penetration of the stab firing pin into the delay ignitor. In at least some instances, the guide stop comprises a first surface complementary to a second surface of the stab firing pin, such that the first surface is operable to engage the second surface of the stab firing pin so as to limit penetration of the stab firing pin into the delay ignitor. The guide stop may improve reliability of rocket motor assembly by preventing over-penetration of the stab firing pin into the delay ignitor.

According to at least one aspect of the present disclosure, a rocket motor assembly is provided that includes a rocket motor propellant and a rocket motor ignitor assembly according to the present disclosure.

FIG. 1 depicts a top view of a shoulder-fired rocket system 100 according to at least one instance of the present disclosure. The shoulder-fired rocket system 100 may be, for example, a rocket propelled grenade system or another shoulder-fired rocket system. One of skill in the art will appreciate that the presently disclosed rocket motor ignitor assemblies, as well as any rocket motor assemblies that include the presently disclosed rocket motor ignitor assemblies, may be used in a wide variety of shoulder-fired rockets and shoulder-fired rocket systems.

As depicted in FIG. 1, shoulder-fired rocket system 100 includes a rocket motor assembly 150 having a proximal end 151 and a distal end 152. The proximal end 151 of the rocket motor assembly 150 may be operably coupled to a warhead 125 and the distal end 152 of the rocket motor assembly 150 may be operably coupled to an expelling charge 175. The expelling charge 175 can be operable to expel the rocket propelled grenade out a launch tube (not shown) upon the actuation (e.g., firing) of the rocket propelled grenade by a user. The expelling charge 175 can be a pyrotechnic composition including, but not limited to, black powder operable to generate a small and/or short-term thrust from gas generation. In some instances, the expelling charge 175 of the shoulder-fired rocket system 100 can include one or more fins and/or thrust directional devices operable to introduce longitudinal rotation or spin of the shoulder-fired rocket system 100 to improve accuracy.

After the shoulder-fired rocket system 100 is launched by being expelled from the launch tube by the expelling charge 175, the rocket motor assembly 150 can ignite to propel the rocket propelled grenade, including the warhead 125, to its target. In at least one instance, the rocket motor assembly 150 can ignite after a predetermine time following the actuation of the expelling charge 175. The rocket motor assembly 150 can include a rocket motor ignitor assembly 155 that is operable to ignite rocket motor propellant in the rocket motor assembly 150.

FIG. 2 depicts an exploded view of shoulder-fired rocket system 100, according to at least one instance of the present disclosure. The shoulder-fired rocket system 100 can include the warhead 125, the rocket motor assembly 150, and/or the expelling charge 175. In at least one instance, the expelling charge 175 can have a threadable and/or threading engagement with the rocket motor assembly 150. The rocket motor assembly 150 incudes motor ignitor assembly 155 that is described further in FIGS. 3-7.

The warhead 125 can be operable to actuate at a predetermined time, predetermined distance from a target (e.g., proximity detonation), and/or upon impact with a target. The warhead 125 can have any number of chemistries, charges, and/or desirable detonation patterns.

FIG. 3 depicts a cross-sectional view of a rocket motor assembly 150, according to at least one instance of the present disclosure. The rocket motor assembly 150 can include a housing 305 that houses a rocket motor propellant 360 as well as a rocket motor ignitor assembly 155. In at least one instance, the rocket motor propellant 360 is a solid fuel grain.

The rocket motor ignitor assembly 155 can include a stab firing pin 310, biasing element 315, guide stop 320, delay ignitor 330, and/or a black powder puck 340. As can be appreciated in FIG. 3, the rocket motor ignitor assembly 155 is depicted in a pre-fired (e.g., ready) condition.

Upon actuation (e.g., firing) of an expelling charge, such as expelling charge 175 shown in FIGS. 1-2, coupled with a distal end 152 of the rocket motor assembly 150, the stab firing pin 310 can overcome the bias of biasing element 315 and travel toward the delay ignitor 330. Upon contact with the delay ignitor 330, the stab firing pin 310 can activate the delay ignitor 330 which can ignite a black powder puck 340 which in turn ignites the rocket motor propellant 360. Ignition of the rocket motor propellant 360 can propel the warhead, such as warhead 125 depicted in FIGS. 1-2, attached to the proximal end 151 of rocket motor assembly 150, to the target.

The rocket motor assembly 150 can include nozzle 370, nozzle channel 372, and/or a nozzle plug 374 operable to direct thrust generated by the firing of the rocket motor assembly 150. The nozzle plug 374 can be operable to protect the nozzle 370 and/or the nozzle channel 372 from particulate prior to firing.

FIG. 4 depicts an exploded view of an ignitor body 465 of a rocket motor ignitor assembly 155, according to at least one instance of the present disclosure. The rocket motor ignitor assembly 155 includes a ignitor tube (e.g., ignitor body) 465 that houses a stab firing pin 310 having one or more relief grooves 380 cut into the side of the stab firing pin 310. The ignitor tube 465 also houses a biasing element 315, a guide stop 320, and delay ignitor 330. FIG. 6 depicts a plan view of a rocket motor ignitor assembly 155 having an ignitor tube 465 housing the stab firing pin 310, biasing element 315, guide stop 320, and delay ignitor 330, as shown in FIG. 4.

FIGS. 5A and 5B depict a rocket motor ignitor assembly 155 in both a pre-fired (e.g., ready) condition (FIG. 5A) and in a firing condition (FIG. 5B), according to at least one instance of the present disclosure. FIG. 6 illustrates a plan view of an ignitor tube body 465, according to at least one instance of the present disclosure. As shown in FIG. 5A, when the rocket motor ignitor assembly 155 is in the pre-fired (e.g., ready) condition, the biasing element 315 is biased against stab firing pin 310, thereby keeping the stab firing pin 310 separated from the delay ignitor 330. FIG. 5B depicts the rocket motor ignitor assembly 155 in a firing condition. As shown in FIG. 5B, when the rocket motor ignitor assembly 155 is in a firing condition, the stab firing pin 310 overcomes the bias of biasing element 315 and translates toward the delay ignitor 330 as a result of the ignition of an expelling charge. The ignition of the expelling charge 175, shown in FIGS. 1 and 2, causes an acceleration sufficient to compression and/or otherwise overcome the bias of the biasing element 315. When the stab firing pin 310 contacts the delay ignitor 330, the delay ignitor 330 activates to cause ignition of the black powder puck 340, which in turn ignites the rocket motor propellant 360, thereby propelling the rocket motor assembly 150 towards the target.

As depicted in FIG. 5B, in some instances, the stab firing pin 310 can include one or more relief grooves 380 which are operable to allow air to vent around the edge of the stab firing pin 310 as the stab firing pin 310 travels toward the delay ignitor 330.

FIG. 7 illustrates a stab firing pin having one or more relief grooves 380, according to at least one instance of the present disclosure. The relief grooves 380 are operable to prevent the stab firing pin 310 from compressing air as it travels within the inner bore 390 towards the delay ignitor 330. Compressing air within the inner bore 390 could increase resistance and/or stiffness to the system which may cause the rocket motor ignitor assembly to fail to ignite in cases of low muzzle velocity launches. The relief grooves 380 can improve safety of the rocket motor ignitor assembly 155 and/or the rocket motor assembly 150. The relief grooves 380 also serve to improve reliability of the rocket motor ignitor assembly 155 by reducing the probability of the stab firing pin from becoming stuck and/or otherwise retarded during its rearward travel towards the delay ignitor 330. In at least some instances, the relief grooves 380 may be helically arranged relief grooves that are cut and/or otherwise formed into the sides of stab firing pin 310 in a helical fashion. Helical relief grooves 380, such as those depicted in FIG. 5B and in close-up view in FIG. 7, can improve the reliability of rocket motor assembly 150, especially when parts are not manufactured to perfect roundness or otherwise contain surface imperfections.

According to at least one aspect of the present disclosure, the stab firing pin 310 may have a length to diameter ratio greater than two (2). Stab firing pins 310 having a length to diameter ratio greater than two (2) ensures that the stab firing pin stays straight as it travels down the inner bore 390 of the ignitor tube body 465, thus improving the reliability of rocket motor assembly 150 and rocket motor ignitor assembly 155. In at least some instances, the stab firing pin 310 may have a length to diameter ratio greater than two and a half (2.5), or greater than three (3).

According to at least one aspect of the present disclosure, rocket motor ignitor assembly 155 includes a guide stop 320 having an inner bore operable to receive the stab firing pin 310 so as to limit penetration of the stab firing pin into the delay ignitor 330. In some cases, the guide stop 320 may be disposed about an exterior surface of the delay ignitor 330. In other cases, the guide stop 320 may be coupled with the delay ignitor 330 and/or the biasing device 315. Over-penetration of the stab firing pin 310 into the delay ignitor 330 is a source of mis-fires. Therefore, guide stop 320 may improve reliability of rocket motor assembly 150 by preventing over-penetration of the stab firing pin 310 into the delay ignitor 330. In at least some instances, guide stop 320 comprises a first surface complementary to a second surface of the stab firing pin, such that the first surface is operable to engage the second surface of the stab firing pin so as to limit penetration of the stab firing pin 310 into the delay ignitor 330. 

What is claimed is:
 1. A rocket motor ignitor assembly comprising: a delay ignitor operable to ignite a rocket motor propellant; a stab firing pin operable to activate the delay ignitor by contacting the delay ignitor; and a biasing element coupled with the stab firing pin, wherein the delay ignitor is operable to ignite the rocket motor propellant after a predetermined amount of time upon contact by the stab firing pin; wherein the biasing element is biased to space apart the stab firing pin and the delay ignitor when the rocket motor assembly is in a pre-fired condition and the stab firing pin is operable to contact the delay ignitor when the rocket motor assembly is in a firing condition.
 2. The rocket motor ignitor assembly according to claim 1, wherein the stab firing pin has a length and a diameter, the length to diameter ratio being greater than
 2. 3. The rocket motor ignitor assembly according to claim 2, wherein the stab firing pin length to diameter ratio is greater than 2.5.
 4. The rocket motor ignitor assembly according to claim 2, wherein the stab firing pin length to diameter ratio is greater than
 3. 5. The rocket motor ignitor assembly according to claim 1, wherein the stab firing pin comprises one or more relief grooves operable to vent air around the edge of the stab firing pin.
 6. The rocket motor ignitor assembly according to claim 5, wherein the relief grooves are operable to reduce air compression between the stab firing pin and the delay ignitor as the stab firing pin travels toward the delay ignitor.
 7. The rocket motor ignitor assembly according to claim 5, wherein the relief grooves are helically arranged.
 8. The rocket motor ignitor assembly according to claim 5, wherein the relief grooves are air venting relief grooves.
 9. The rocket motor ignitor assembly according to claim 5, wherein the relief grooves are cut into an outer surface of the stab firing pin.
 10. The rocket motor ignitor assembly according to claim 1, wherein the rocket motor ignitor assembly comprises an ignitor tube, wherein the delay ignitor, the stab firing pin, and the biasing element are disposed within an inner bore of the ignitor tube.
 11. The rocket motor ignitor assembly according to claim 10, wherein the stab firing pin and the biasing element are retained within the ignitor tube, the stab firing pin having one or more relief grooves formed therein operable to allow air between the stab firing pin and the delay ignitor to vent past the stab firing pin when the stab firing pin translates toward the delay ignitor within the inner bore.
 12. The rocket motor ignitor assembly according to claim 1, further comprising a guide stop disposed about an exterior surface of the delay ignitor, wherein the guide stop comprises an inner bore operable to receive at least a portion of the stab firing pin therethrough so as to limit penetration of the stab firing pin into the delay ignitor.
 13. The rocket motor ignitor assembly according to claim 12, wherein the guide stop comprises a first surface complementary to a second surface of the stab firing pin, such that the first surface is operable to engage the second surface of the stab firing pin so as to limit penetration of the stab firing pin into the delay ignitor.
 14. The rocket motor ignitor assembly according to claim 12, wherein the guide stop is operable to prevent over-penetration of the stab firing pin into the delay ignitor.
 15. The rocket motor ignitor assembly according to claim 1, wherein the rocket motor assembly is in a firing condition upon the ignition of an expelling charge coupled with the rocket motor ignitor assembly.
 16. The rocket motor ignitor assembly according to claim 1, wherein the rocket motor ignitor assembly is for use in a shoulder-fired rocket system.
 17. The rocket motor ignitor assembly according to claim 16, wherein the shoulder-fired rocket system is a rocket propelled grenade system.
 18. A rocket motor assembly comprising: a rocket motor propellant; a delay ignitor operable to ignite the rocket motor propellant; a stab firing pin operable to activate the delay ignitor by contacting the delay ignitor; and a biasing element coupled with the stab firing pin, wherein the delay ignitor is operable to ignite the rocket motor propellant after a predetermined amount of time upon contact by the stab firing pin; wherein the biasing element is biased to space apart the stab firing pin and the delay ignitor when the rocket motor assembly is in a pre-fired condition and the stab firing pin is operable to contact the delay ignitor when the rocket motor assembly is in a firing condition.
 19. A shoulder-fired rocket system comprising: a rocket motor assembly, the rocket motor assembly comprising: a rocket motor propellant; a delay ignitor operable to ignite the rocket motor propellant; a stab firing pin operable to activate the delay ignitor by contacting the delay ignitor; and a biasing element coupled with the stab firing pin, wherein the delay ignitor is operable to ignite the rocket motor propellant after a predetermined amount of time upon contact by the stab firing pin; wherein the biasing element is biased to space apart the stab firing pin and the delay ignitor when the rocket motor assembly is in a pre-fired condition; an expelling charge coupled with a distal end of the rocket motor assembly; and a warhead coupled with a proximal end of the rocket motor assembly.
 20. The shoulder-fired rocket system of claim 19, wherein upon actuation of the expelling charge, the stab firing pin is operable to contact the delay ignitor. 